1' dia

1
HISTOLOGY 1.13. NERVOUS TISSUE
Nervous tissue is specialized to generate and
conduct impulses. Origin neuroectoderm Tissue
components nerve cells, glial cells and their
processes Blood supply densely capillarized
2
The neuron Generalized schematic drawing of a
multipolar neuron
Nissl staining
Silver impregnation
3
Classification of neurons on the basis of their
processes
Unipolar neurons Pseudo-unipolar neurons
Bipolar neurons
4
Classification of neurons on the basis of their
processes
Motoneuron in the spinal cord (Nissl staining)
MULTIPOLAR NEURON-TYPES
Cortical pyramidal cell (silver impregnation)
Cerebellar Purkinje cell
5
Classification of neurons on the basis of their
activity
Excitatory cell type it has spiny dendrites,
its axon makes asymmetrical synapses using
excitatory neurotransmitters
Inhibitory cell type it has non-spiny beaded
dendrites, its axon makes symmetrical synapses
using inhibitory neurotransmitters
6

• Model of a multipolar neuron
• Within the nervous tissue
• Dendrite
• Axon (myelinated)
• Nucleus
• Nucleolus
• Golgi apparatus
• rER
• Axon hillock and initial segment
• Synaptic boutons terminating
• on the membrane of the neuron
• 9. Glial cell endfeet
• 10.Capillary with erythrocytes
• 11. Compact neural tissue (neuropil)

7
Cell body (perikaryon) of the neurons (electron
micrograph)
Nnucleus nnucleolus Asterisks label stacks of
rER (Nissl bodies) Mmitochondrion Llipofuchsin G
Golgi apparatus Non-visible on
the picture microtubules neurofilaments sER
EM
LM
G
M
L
8
Processes of the neurons dendrites
Cross-section
Highly branched processes. Dendrites may contain
microtubules, neurofilaments, sER, free
ribosomes and mitochondria. Their membranes
exhibit postsynaptic densities (arrows), the
sites of synaptic transmission, thus dendrites
are the receiving processes, accepting
impulses from other neurons.
Transverse section
9
Processes of neurons axons
Long, cylindrical process with few branches
along its course and multiple terminal
branches (telodendrion).
Axons originate from axon hillock. Initial
segment free of myelin sheath, receive
synapses from other neurons.
Axon hillock
Initial segment
LM
Axon
Terminal bulb, or synaptic bouton
Telodendrion
EM
10
Characteristics of dendrites and axons a summary

• Axon Dendrite
• Extends from cell body or dendrite extends from
  cell body
• Begins with initial segment in proximal portion
  continues cytoplasm
• May be absent (amacrine cells) May be absent
  (dorsal root ganglion)
• Unique in most cells Usually multiple
• May be myelinated or no Rarely myelinated
• Never contains ribosomes Contain rER, or
  ribosomes
• Smooth contours, cylindrical shape Irregular
  contours, appendages (spines)
• The thinnest process at the origin Originates as
  thick, tapering process
• Ramifies by branching at obtuse angles Ramifies
  by branching at acute angles
• Gives rise to branches of same diameter Subdivides
  into smaller branches
• May extend long distances from soma Confined to
  the vicinitiy of cell body
• Neurofilaments predominate in axons Microtubules
  predominate in dendrites
• Capable of generating action potentials Conduct
  in a decremental fashion
• propagating them and synaptic but may be
  capable of generating
• transmission action potentials
• 14.Primarily engaged with conduction Primarily
  engaged with receiving
• and transmission synapses

11
Synapses A synapse between neurons is a site of
morphological specialization where one neuron is
able to influence the excitability of another
neuron. Types of synapses 1./ Electrical
synapse is a gap junction between the membranes
of two adjacent neurons 2./ Chemical synapse
changes the membrane potential of the
postsynaptic neuron by releasing neurotransmitter
molecules.
Electrical synapse (gap junction)
Chemical synapse
12
Types of chemical synapses A./ On the basis of
the postsynaptic site
Axo- spinous
Axo- dendritic
(Less frequent types /not shown here/ Axo-axonic
synapse, Dendro-dendritic synapse, Dendro-axonic
type Reciprocal synapse)
Axosomatic
13
Types of chemical synapses A./ On the basis of
the function
1./ Excitatory (arrow) Usually
asymmetrical 2./ Inhibitory (hands) Usually
symetrical
14
Neurotransmitters of the chemical
synapses Acetyl choline (ACh) Amino
acids glutamate (Glu) Amino acid derivatives
serotonin (5-HT) aspartate (Asp) dopamine
(DA) glycine (Gly) g-amino butyric acid
(GABA) histamine (His) Peptides opioids
(enkephalins, endorphins, dynorphins,
etc.) neurohypophyseal (vasopressin, oxytocin,
neurophysin) tachikinins (substance P and K,
neurokinin, etc.) gastrins ( gastrin,
cholecystokinin-CCK) Somatostatin
(SOM) Vasoactive intesitnal polypeptide
(VIP) Neuropeptide Y (NPY) etc. Purins aden
osin